Copper conductor coated with silicone resin composition



States Patent COPPER CONDUCTOR COATED WITH SILICONE RESIN COMPUSITION NoDrawing. Application July 12, 1954 Serial No. 442,894

2 Claims. ((11. 117-232) This invention relates to improved siliconewire enamels and to copper wire and other conductors coated therewith.

The use of pure silicone resins for the provision of Wire enamelsresistant to high temperature exposures has long been desired. Therehave been several disadvantages, however, in connection with theapplication of such resins to bare copper wire and other copperconductors. For one thing, the copper acts as an inhibitor and retardsor prevents satisfactory curing of the resins, thereby entailing slowapplication speeds and poor solvent resistance. For another, the copperitself is subject to oxidation, presumably due to the porosity orbreathing effect of the undercured silicone film.

Most of the above disadvantages have been overcome to a large measure byusing silicone copolymers in place of pure silicones. While the heatresistance is thereby reduced to some extent, it has proven to besuperior to that of most purely organic films. For nominal filmthicknesses the copolymer type of material has proven to be of distinctadvantage. However, when heavy film thicknesses such as those in theso-called double-build class are desired, defects traceable to oxidationof the copper are encountered, presumably as a result of the multipleexposure of the coated wire to high curing temperatures. The oxidationincreases with each succeeding coat, and very poor adhesion andapparently brittle films result, all presumably due to poor cure of theenamels constituting the successive coats.

We have now found that the incorporation of certain amines in thesilicone and silicone-copolymer enamels prevents oxidation of the copperand overcomes the inhibiting effects of copper on the cure of theenamels.

Accordingly, it is an object of this invention to provide improvedsilicone-containing Wire enamels protected against the cure-inhibitingeffects of copper.

It is a further object to provide improved silicone copolymer wireenamels containing protective amounts of certain organic amines.

Another object is to provide coated copper wire having double-buildthicknesses of silicone-containing enamel thereon and free of defectsresulting from oxidation of the copper during the coating treatment.

Still another object is to provide coated copper wire of the type lastdescribed having good heatand solventresistance with good flexibilityand adhesion in the enamel coating thereof.

These and other objects will be apparent from the following detaileddescription of the invention.

The U. S. Patent No. 2,663,694 of Millar and his copending applicationSerial No. 320,120, filed November 12, 1952, now Patent No. 2,768,149,describe and claim heat-resistant silicone coating compositions whichhave been prepared by cobodying selected silicones with selected alkydresins, thereby yielding what is here termed a silicone copolymer resin.Other silicone-alkyd copolymer resins are described in the U. S. PatentNo. 2,587,295 of Doyle, the U. S. Patent No. 2,517,777 of Fenn et al.,the U, S. Patents Nos. 2,502,286 and 2,605,243 of Sowa,

the U. S. Patents Nos. 2,584,340, 2,584,341, 2,584,343 and 2,589,243 ofGoodwin et al, and the British Bowman Patent No. 583,754. Other siliconecopolymers can also be benefited by the present invention, such as thesiliconepolyvinyl acetal copolymer of U. S. Patent No. 2,506,320. In allsuch copolymer coatings, the benefits begin to be come apparent when thesilicone content of the cured coating approaches about 20% of the totalweight of resin solids in the cured coating, and are of readysignificance when the silicone content is a major percentage of theresin solids.

Any of the pure silicone heat-hardenable coatings of the polysiloxaneand polysilane types can be significantly benefited by applying theprinciples of the present invention. The hydrocarbon substituents of thesilicon atoms in these coatings can be aliphatic or cyclic or both andeither saturated or unsaturated, or both. These substituents can amountto between A2 and 2 groups per silicon atom, but more preferablyconstitute between 1 and 2 groups per silicon atom. The following U. S.patents disclose a wide variety of pure silicone heat-hardenable,hydrocarbon-substituted polysiloxane and/ or polysilane resinsappropriate for use as resins in wire enamels and comparable coatings:Reissue No. 23,060, 2,258,218, 2,258,219, 2,258,220, 2,258,221,2,258,222, 2,476,132, 2,486,162, 2,494,920, 2,495,306, 2,506,320,2,507,516, 2,516,047, 2,517,777, 2,518,160, 2,521,672, 2,523,037,2,528,615, 2,542,641, 2,550,003, 2,563,005, 2,571,533, 2,584,835,2,588,393, 2,590,957, 2,595,727, 2,598,402, 2,605,194 and others.

Any of said resins can be utilized in the present invention byincorporating therewith one or more of the amines which we havediscovered to be effective in inhibiting the oxidation of copper and thecure-impairing effects of copper on pure silicone and silicone-copolymerresins.

The amines last referred to are triethanolamine, phenylbeta-naphthylamine, and butoxy methyl melamine. The latter is available commerciallyunder the proprietary name of Resimene 878 and is a mixture of butylethers of the various methylol groups occurring in melamine-formaldehydecondensation products. These amines have been found to be specific intheir effects as shown by our discovery that amines of closely similarcompositions are ineffective; e. g., diethanolamine andphenyl-alpha-naphthyl amine. In our investigations we have testednumerous other amines, none of which had any noticeable elfect for ourpurposes.

The three amines mentioned above are employed in amounts between about1% and 20% by weight of the silicone resin, each amine having an optimumvalue within this range which is difierent than the optimum value forthe others. In silicone-copolymer resins, triethanolamine is preferablyemployed in amounts between 5 and 10%, while phenyl-beta-naphthylamineis employed in amounts between about 4% and 8%. Resimene 878 ispreferably used in amounts between about 9% and 12%.

We are presently unable to give any suitable explanation for thespecificity of these amines for our purposes. The following examplesillustrate their obvious effectiveness, however.

Example 1 A wire coating was prepared from the following ingredients:

The triethanolamine here amounts to 7% by weight on the solids of thesilicone alkyd. This coating was ap- 5. plied to copper wire in eightpasses to give a coating thickness of .0020", the coating which wasapplied at each pass being cured at approximately 1000 F. for 9 secondsbefore the next pass. Examination of the finished wire revealed that thecoating had excellent adhesion and flexibility, and was free of sleevingand copper oxidation. In a comparable run employing the same coatingminus the triethanolamine, oxidation and improper cure of underlyingcoats became evident between the 7th and 8th pass. When the coated wirewas subjected to a snap test, indications of sleeving and consequentlack of adhesion were apparent.

The silicone alkyd of the above composition was prepared as follows:

A. An alkyd was prepared by mixing 31 parts of 2 ethyl hexoic acid, 29.9parts of glycerine, C. P., 39.1 parts of phthalic anhydride and 3.5parts of xylol. The mixture was heated to reflux in a C atmosphere andwas refluxed at about 460 F. with a Water trap in the system until aboutparts of water had been separated and the resin had an acid number of 4or under. The resin. was reduced finally with 35.8 parts of xylol, togive a solids content of 6970 and a viscosity of 2 -2 A 70% N. V. M.silicone resin solution in xylol was prepared by hydrolyzing andcondensing an equal molar mixture of phenyl trichlorosilane, methyltrichlorosilane, and monophenyl monomethyl dichlorosilane so as toproduce a product having a total of 1 /3 methyl and phenyl radicals persilicon atom, an equal number of methyl and phenyl radicals and ahydroxyl content of 3.61% by weight of resin solids. This siloxanol wasproduced by hydrolyzing the said equimolar mixture by adding it to anagitated mixture of water and toluol. The water was employed in amountsufliciently in excess of that requisite for hydrolysis that thehydrogen chloride produced and dissolved in the excess water would givea percent by weight aqueous hydrochloric acid. The toluol Was employedin amount to yield a percent by weight solution of siloxane resin in thetoluol. The resin was transferred to Xylol by adding enough xylol toyield a 70 percent solution therein and removing the toluol by vacuumdistillation.

The above alkyd and the above silicone resin solution were mixedtogether in the proportions of 496 parts by weight of the former to 577parts by weight of the latter. The resulting mass was refluxed until a Zviscosity at 65% N. V. M. had been attained, then the mass was cooled to220 F. and reduced to N. V. M. with 429 parts of xylol. The reducedsolution had an acid number of 2, a viscosity of G-H, and had a weightof v 8.55 lbs. per gallon. To each five gallons of the 50% solution wasadded 1 /3 liquid ounces of a lead and manganese naphthenate drierhaving 4.5% and 96% by weight of lead and manganese respectively.

Example 2 The triethanolamine of Example 1 can be replaced with 6% byweight on the silicone alkyd solids of phenyl-beta napht'nyl amine togive substantially identical results.

Example 3 ings plus the presently unneeded high heat resistance of thesecoatings have been a deterrent to their use apart from certainshortcomings which they possess. Accordingly, present demands favor thelower priced, moderately-heat-resistant coatings of the siliconecopolymer class.

The art of making alkyd resins which are appropriate for use inpreparing silicone-copolyrners is amply disclosed in the various patentsand patent applications identified above, and needs little furtherdiscussion here other than to make it clear that the formulation of thealkyds can be very broad in respect to the kinds and proportions of rawmaterials employed therein. Thus any of the usual polyhydric alcohols,polycarboxylic acids, fatty acids, glyceride oils or oil acids andsolvents commonly used in alkyd resins can be used in the alkyds of thesilicone-copolyrner resins of this invention as long as compatibility ofthe alkyd and silicone is secured in the completed silicone-copolymerresin(s).

A wide choice of silicones can also be exercised in selecting thesilicone component or components of the silicone-copolymers. As the artalready knows, the selected silicone(s) and alkyd(s) must be processedin appropriate manners to provide a finished product in which bothcomponents are compatible. The patents and patent application identifiedabove describe these and other aspects so fully that no furtherdiscussion here seems warranted.

In view of the wide choice of resins to which this invention can beapplied, it will be clear that the minor amount of amine(s) which isincorporated therewith to secure the benefits of the present inventionis also subject to wide variations. In addition to varying with theformulation of the particular coating at hand, it varies also with thecuring temperatures used, with the time cycle of the coating procedure,with the degree of oxidation-inhibition which is needed or desired, andwith the particular amine or mixture of amines that one chooses to use.Accordingly, little can be said in a definite way as to the amount ofamine(s) to be incorporated, and the chosen amount should be that whichbest serves the need at hand. An appropriate selection of amount on suchbasis is well within the ability of one skilled in the art, as will bereadily recognized.

While the present invention pertains mostly to the commercial coating ofcopper wire, e. g., magnet wire, it can obviously be appliedadvantageously in the coating of any form of copper whether electricalcopper or otherwise where a durable, protective, heat-resistant,heathardened coating is desired. In most of such applications,particularly for electrical copper, the electricalinsulating qualitiesof the coating are of importance. In this connection We have found thatthe incorporation of effective amounts of our amines is baked wire andconductor coatings of the types herein identified does not impair theinsulating quality of the coatings, and in fact, usually improves it asa result of improving the integrity of the applied film(s).

Having now described our invention, what we claim is:

1. A copper conductor coated with a heat-hardened synthetic resincoating of the double-build class, the resin solids of which comprise atleast 20% resinous silicones and about 1-20% by Weight on said siliconesof at least one amine selected from the group consisting oftriethanolamine, phenyl-beta-naphthyl amine arid butoxy methyl melamine.

2. A copper conductor as claimed in claim 1 wherein the resin solids ofsaid coating comprise at least 50% resinous silicones.

References Cited in the file of this patent UNITED STATES PATENTS2,389,807 McGregor et al Nov. 27, 1945 2,500,842 MacKenzie Mar. 14, 19502,528,615 Smith Nov. 7, 1950 2,553,362 Dannenberg May 15, 1951 2,596,450Wachter et al. May 13, 1952 2,611,727 Underwood Sept. 23, 1952 FOREIGNPATENTS 130,397 Australia Dec. 1, 1948

1. A COPPER CONDUCTOR COATED WITH A HEAT-HARDENED SYNTHETIC RESINCOATING OF THE DOUBLE-BUILD CLASS, THE RESIN SOLIDS OF WHICH COMPRISE ATLEAST 20% RESINOUS SILICONES AND ABOUT 1-20% BY WEIGHT ON SAID SILICONESOF AT LEAST ONE AMINE SELECTED FROM THE GROUP CONSISTING OFTRIETHANOLAMINE, PHENYL-BETA-NAPHTHYL AMINE AND BUTOXY METHYL MELAMINE.